How do I see and cancel the approvals I have already given?

The Activities tab on the home screen. History tells you what has happened; this tells you what can still happen — every standing allowance on the current account and network, with the unlimited ones marked.

The list is split into At risk (allowances on tokens you actually hold, which is where the money is) and Dormant (allowances on tokens with no balance behind them). On a real account most approvals turn out to be dormant, so the split is what makes the handful that matter visible.

Revoking is one tap and needs no password — it only ever removes a permission. It is a blockchain transaction, so it costs a network fee and reports pending and then confirmed like any other.

Worth doing occasionally, and worth doing immediately after using a site you have since become suspicious of.